Electrode set and stimulating device

ABSTRACT

The electrode set for a stimulation device, such as a TENS or EMS stimulation device comprises at least a plurality of neighboring electrically active zones close to each other said active zones forming a succession of poles of alternating polarity or being grouped to form groups of poles of alternating polarity, wherein at least one of said active zone or group of zones has a lateral size (D 2 ) of approximately 1 mm to 40 mm, wherein at least one of spacing (D 1 ) between neighboring active zones or groups of zones is approximately of 1 mm to 40 mm, and said set further comprises contacting means connected to said active zones or groups of active zones.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/441,167, filed Apr. 7, 2010, which claims priority to InternationalPatent Cooperation Treaty (PCT) Application No. PCT/IB2007/053701, filedSep. 13, 2007, and to European Patent Application Nos.: 06120599.3,filed Sep. 13, 2006; 07101987.1, filed Feb. 8, 2007; 07105400.1, filedMar. 30, 2007; and 07111474.8 filed Jun. 29, 2007 all of which areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention concerns a stimulation electrode set, for examplean electrode set for TENS or EMS stimulation, and a stimulating devicecomprising such electrode sets.

The present invention also concerns a method for optimizing parametersof electrode sets according to the present invention and treatmentsusing an electrode set according to the present invention.

BACKGROUND OF THE INVENTION

Electrodes and stimulating devices are known as such in the prior artfor different treatments of the human body. An example of anelectrotherapy transducer is given in EP 0 638 330 which comprises asheet of support material with a number of electrodes arranged in amatrix-like structure, adjacent electrodes receiving electric signals ofopposite polarity. In a second embodiment, the structure of theelectrodes is comb-shaped with electrodes being arranged alternately andequally spaced in relation to one another. This electrotherapy device issaid to be used for the treatment of cellulitis or for the treatment ofmuscles but not much more information is given on the structure of thedevice, or on the electrical signals used during a treatment.

In the field of electrical stimulation, two stimulation principles areknown: transcutaneous electrical nerve stimulation (TENS) on the onehand, and electrical muscular-type stimulation (EMS) on the other hand.TENS stimulation devices are used for the treatment of pain whereas EMSstimulation devices are used for physical therapy and body building, forexample for correcting muscle atrophy, stimulating muscle growth andincreasing range of motion.

Devices that apply such TENS and/or EMS stimulations to the body of auser are known per se in the art.

As an illustrative example, application EP 1 095 670 which isincorporated by reference in the present application, describes aneuromuscular electrical stimulator using stimulation electrodes and anelectrical impulse generator. This device is mainly used for EMSstimulation and it comprises at least two electrodes spaced apart andplaced on a part to be treated of the human body. A stimulator isconnected to the electrodes through connection wires and it sends thedesired electrical signals to the electrodes in order to stimulate themuscles.

With specific respect to TENS, this type of treatment has beenextensively described in the art. As a reference, one may cite thepublication “Electrotherapy 11^(th) Edition Evidence-based practice”,October 2001 by Sheila Kitchen, MSc, PhD, DipTP, MSCP, Head, Division ofPhysiotherapy, King's College, London.

Chapter 17 of this publication relates to “Transcutaneous ElectricalNerve Stimulation (TENS)” by Mark Johnson, incorporated by reference inthe present application, and reference is made to this Chapter for thetheory and explanations relating to TENS treatments. As can beunderstood from this publication, TENS is “the most frequently usedelectrotherapy for pain relief, and reference is made to thispublication for the theory explaining and demonstrating the effects ofTENS stimulation and also the theory of “The Pain Gate”.

According to the above-mentioned article of Mark Johnson (see FIG. 17.2)under normal physiological circumstances, the brain generated painsensations by processing incoming noxious information arising fromstimuli such as tissue damage. The noxious information reaches the brainby passing through a metaphorical “pain gate” located in the lowerlevels of the central nervous system. The pain gate may be closed byactivation of various sensory afferents, i.e. through rubbing the skinwhich generates activity in large diameter Aβ afferents which inhibitsthe onward transmission of noxious information.

It is therefore an aim of conventional TENS to selectively activate Aβfibers using electrical currents to provide segmental analgesia.

Another way to close the pain gate is to activate pain-inhibitorypathways which originate in the brain and descend to the spinal cordthrough the brainstem. Accordingly, an aim of AL TENS (Acupuncture-likeTENS) is to activate small diameter peripheral fibres to activate thedescending pain-inhibitory pathways. This stimulation however provokes amuscle contraction.

Another way to produce peripheral blockade of nociceptive afferentactivity and segmental and extrasegmental analgesia is to use IntenseTENS to activate small diameter Aδ cutaneous afferents by deliveringsaid TENS stimulation over peripheral nerves arising from the site ofpain at an intensity which is just tolerable to the patient (usinghigh-frequency and high-intensity currents).

During classical and Intense TENS stimulation programs, it is importantto stimulate only the sensitive nerve cells end not the motor nerves,which will induce a tetanic muscle contraction which can be painful, aneffect contrary to the one sought.

One of the problems to which the user of stimulators is confronted isthe positioning of the electrodes on the body in view of the desiredtreatment and also the sizes of the electrodes used for a giventreatment.

Another example of a stimulation device is given in US 2002/0077688.This publication relates to a body garment which is used in combinationwith an electrical muscle and/or nerve stimulation device. In thispublication, the body garment is specifically structured to position theelectrode pads at predetermined positions on the body corresponding withdifferent muscle or nerve groups and it is connected to a TENS unitcontroller or an EMS unit controller for the desired stimulation. Astaught in this document, the garment may cover the entire body of theuser or only a part of said body.

Another publication of the prior art relating to TENS stimulation is WO2005/002668. In this publication, the problem identified to be solved isadaptation. This occurs when although the amplitude and frequency of thestimulation are subjected to changes, the polarity of the electrodes isnot changed so that the nerve cells which are subjected to the samestimulation adapt to said stimulation. Accordingly, an idea of thispublication is to provide an electrode system with at least two poleswhich are separated by an insulating material to prevent a short-circuitbetween the poles and allowing the poles to be provided with electricalfields by stepwise alternating the negative current from one pole to thenext pole. This causes two different areas to be stepwise treated by theelectrode system. In one embodiment, the system includes four poles suchthat the electrical field may move between the poles. Since the actionpotential is initiated mainly below the negative pole, the treatmentseems to wander over the surface covered by the electrode.

Another publication WO 2005/075018 relates to a device for neuromuscularstimulation. In this publication, the stimulation apparatus comprises anerve stimulation array electrode comprising a substrate for applicationto the skin of a user bearing an array of electrodes arranged to bebrought into electrical contact with the skin of the user, inputcontacts and user operable switch means for making or breaking theelectrical contact between said input contacts and any selected one orones of said electrodes allowing the user to freely form any group ofelectrodes. In addition, the apparatus comprises a separate commonground or counter electrode which will not generally need to be in theform of an array. This design allows in particular the practitioner orthe patient to find which electrodes in the array contribute mosteffectively to producing the desired stimulation effect and he can thusform a specific group accordingly.

Another publication related to TENS treatment is WO 2005/065770. In thispublication, the device comprises a current generating device configuredto generate first and second types of electrical TENS currents. Theconstruction allows a specific localized superficial blockade by anappropriate targeting of the intra epithelial and dermal nerves. Morespecifically, the device further comprises an array of electrodes to beplaced around an injection location on the skin of a patient, said arraybeing electrically coupled to the current generating device. Theelectrodes comprise a first and a second group, the first group beingconfigured to be placed closer than the second group to the injectionlocation on the skin of the patient. Typical sizes of electrodes areapproximately 0.8 mm of width or diameter, an area of approximately 0.5mm² and the distance between the electrode is no more than 2 mm.Preferably, in this publication, the distance is less than 1 mm or evenless than 0.5 mm. The current applying device is configured to apply thefirst type of TENS current to the first group of electrodes and applythe second type of TENS current to the second group of electrodes. Byactivating electrodes in pairs around the injection location, a ring ofdischarge pathways though the patient's skin may be sequentially createdthereby providing a good coverage of the sensory nerves in the area. Thevoltage signals applied to the inner electrodes in particular maydepolarize the nerves within the skin to thereby suppress painsensitivity.

Other examples of TENS treatment devices and method are described inpublications WO 93/22966, U.S. Pat. No. 5,785,040, U.S. Pat. No.6,301,500 and US 2002/0055762. The content of all publications citedabove are incorporated by reference in the present application.

Another field using electrodes applied to a patient is iontophoresis.This technique is generally defined as a non-invasive method ofpropelling high concentrations of a charged substance, normallymedication or bioactive-agents, transdermally by repulsive electromotiveforce using a small electrical charge applied to an iontophoreticchamber containing a similarly charged active agent and its vehicle.Although using electrodes as well, this method and the devices used arein fact very different from methods and devices used in the field ofTENS or EMS stimulation, in particular because of the effect sought andprinciple of functioning of the respective devices.

Such iontophoretic devices are used for example to inhibit perspirationfrom human hands, feet or underarms and also for the treatment of varieddermato logic and cosmetic problems.

Use of an iontophoretic device is for example described in U.S. Pat. No.4,164,226. In this patent, the device comprises intermingled negativeand positive electrodes (forming an array) all having porous material tocarry out the iontophoretic effect.

WO 93/00959 shows another device and method to deliver topical drugs toan area of tissue to be treated by iontophoresis. In this publicationthe electrodes are made by two electrode patterns each including a setof substantially parallel electrodes being arranged in an alternatingarrangement.

Other devices described in US 2002/055703 and U.S. Pat. No. 5,968,006are used both for iontophoresis and electroporation. In bothpublications, an electrode structure has the shape of interdigitatedcomb-like electrode pairs. However, in such field, the use of electrodesis combined with a porous material or a chamber to carry out theiontophoretic effect and the electrical signal is not used to stimulatenerves or muscles as in a TENS or EMS system.

SUMMARY OF THE INVENTION

According to the principle of the invention, for a TENS stimulation, oneuses electrodes of small surface, close to each other. Indeed, in thiscase, the density of current generated remains constant in a small depthof skin under the electrode and it diminishes quickly by currentdispersion, such that the effective stimulation remains close to thesurface.

Conversely, in muscular stimulation programs, one wants to go deeper inorder to affect the muscles. To this effect, one rather uses electrodeswith a larger surface such that the constant current density under theelectrode penetrates deeper in the skin before its dispersion.

Similarly, depending on the type of stimulation desired (TENS or EMS),the relative position of the electrodes has an importance. For a TENSstimulation, the two electrodes should be closer to each other whereasfor EMS stimulation, the two electrodes should be spaced apart.Moreover, the position of electrodes cannot be chosen arbitrarily inthat if they are too close, the stimulation may not penetrate enough inthe body of the user to achieve the desired stimulation.

Also, as can be understood from previous designs, the proper positioningof at least two separate electrodes might be a problem for a user.

It is therefore an aim of the present invention is to improve the knownsystems.

More particularly, an aim of the invention is to provide an electrodestructure that is more efficient for TENS stimulation and easy to use.

Another aim of the present invention is to provide a system that iscapable of carrying out TENS or EMS stimulation.

A further aim of the present invention is to provide a system able toprioritize the stimulation of either sensitive or motor nerves asdesired.

A further aim of the present invention is to propose a method foroptimizing parameters of the electrode system in order to obtain a moreefficient device than previously known.

A further aim of the present invention is to propose a stimulationmethod that uses the features of the electrode set according to thepresent invention.

An idea of the present invention is to form an electrode set with activezones of reduced surface area which are close to each other rather thantwo electrodes of a larger surface area that are distant such as ispresently done. In a more detailed manner, the present inventionprovides optimized sizes and dimensions for the active zones forming theelectrode. In the present invention, the notion of electrode should beinterpreted in a broad sense as meaning a zone which is able to apply anelectrical potential directly or indirectly to the body of the user.

The set of electrodes is used with a stimulator that is connected to theactive zones, for example through cables or other suitable equivalenttransmission means.

In one embodiment, one forms an electrode set with active zones that areintermingled in which one may choose freely the polarity of the injectedcurrents thus forming a set of electrodes with alternating poles.

These active zones can be mounted on an isolating support backing (forexample a fabric or another equivalent means) and then placed directlyon the part of the body to be stimulated. This backing may be oversizedin order to improve adhesion of the set to the skin.

In a variant, one uses a gel layer placed between the active zones andthe surface of the body. The gel layer can be a continuous layer definedaccording to the parameters disclosed below and in reference to FIGS.10A-15, or a gel layer placed only over the surface of the active zonesor even a gel paste or another conductive fluid.

The stimulator may be able to activate all the active zones of the set,or only a determined group. Accordingly, one may choose either adetermined group, that is at least two active zones of opposite polaritywhich are close to each other (for example neighboring) if one wishes tostimulate preferably the sensory fibers or at least two active zones farapart from each other if one wishes to obtain a muscle stimulation.

Several embodiments and variants of the invention will be illustrated inthe following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be best understood by the description of severalembodiments and of the corresponding drawings in which

FIG. 1 shows a first embodiment of an electrode set viewed from below;

FIG. 2 shows a second embodiment of an electrode set viewed from below;

FIG. 3A shows a lateral cut view of the set of FIG. 2;

FIG. 3B shows a lateral cut view of a variant of the set of FIG. 2;

FIG. 4 shows a partial view of the set of the first or secondembodiments;

FIG. 5 shows another embodiment of the set of the invention;

FIGS. 6A to 6D illustrate in a schematical way different shapes ofactive zones;

FIGS. 7A and 7B show other embodiments of the invention;

FIG. 8 illustrate a possible use of the electrode set according to thepresent invention;

FIGS. 9A and 9B illustrate alternate embodiments of a set according tothe present invention with a stimulator;

FIG. 10A illustrates a model for dimensioning an electrode set accordingto one embodiment of the present invention.

FIG. 10B illustrates a top view of the model shown in FIG. 10A.

FIG. 11 illustrates a circuit associated with the model.

FIG. 12 illustrates a simplified version of the circuit shown in FIG.11.

FIG. 13 illustrates a diagram associated with the model.

FIG. 14 illustrates an electrical diagram associated with the model.

FIG. 15 illustrates three possibilities of stimulation associated withthe model.3

FIG. 16A is a table illustrating TENS thresholds for various sizes andspacings of electrodes for a first patient.

FIG. 16B is a table illustrating MOTOR thresholds for various sizes andspacings of electrodes for the first patient.

FIG. 16C is a table illustrating ratio thresholds (MOTOR/TENS) forvarious sizes and spacings of electrodes for the first patient.

FIG. 17A is a table illustrating TENS thresholds for various sizes andspacings of electrodes for a second patient.

FIG. 17B is a table illustrating MOTOR thresholds for various sizes andspacings of electrodes for the second patient.

FIG. 17C is a table illustrating ratio thresholds (MOTOR/TENS) forvarious sizes and spacings of electrodes for the second patient.

FIG. 18A is a table illustrating TENS thresholds for various sizes andspacings of electrodes for a third patient.

FIG. 18B is a table illustrating MOTOR thresholds for various sizes andspacings of electrodes for the third patient.

FIG. 18C is a table illustrating ratio thresholds (MOTOR/TENS) forvarious sizes and spacings of electrodes for the third patient.

DETAILED DESCRIPTION

In the first embodiment of FIG. 1, one has represented a view from below(that is the side that will be in contact with the skin of the user) ofan electrode set according to the invention. This set has two elements1, 2 having a succession of intermingled active zones (having arectangular shape in this FIG. 1A, 1B, 1C, 1D, 2A, 2B, 2C, 2D and a base1E, 2E. The two elements 1, 2 are mounted on a first non-conductivelayer 3 (for example a flexible fabric layer) and are connected each tocontacting means 4, 5 for example wires for connection to a stimulator(not shown). In one embodiment, the wires 4, 5 are connected to therespective bases 1E, 2E. In the representation of FIG. 1, the activezones 1A-1D, 2A-2D have alternating polarities.

In some embodiments, the set represented comprises a lateral screen madeof a non-conductive material and placed on the bases 1E, 2E of the setso that only the active zones 1A-1D, 2A-2D are in contact with the skinof the user.

It is of course understood that the screen is optional and that in otherconfigurations, the set can be provided without such screen.

In FIG. 1, no gel has been represented but a gel layer may be providedat least over the active zones 1A-1D, 2A-2D. In some embodiments, asingle gel layer covers all the active zones and the screen if present.In a variant, the gel layer is only present on the active zones.

In FIG. 2, another embodiment is illustrated.

In this embodiment, a first non-conductive layer 3 (for example afabric) is prepared. On this non-conductive layer 3, a layer of moderateconductive carbon 6 is placed, said layer 6 being cut to form the activezones 7 and 8. Over this layer 6, in order to effectively form theactive zones, a printing of conductive ink (for example a silver-basedink or paint) is carried out on each active zone 7, 8. In addition, inorder to connect the active zones 7, 8 to the wires 4, 5, a strip 9, 10of conductive ink is also applied on both sides of the carbon layer.Finally, insulating layers 11, 12 (such as a screen) are applied on bothsides of the carbon layer 6. The connection of the wires 4, 5 to thestrips 9, 10 are for example made by gluing the end of the wires to thestrips. Of course, other equivalent procedures are possible such as snapconnectors. In the representation of FIG. 2, the side of the wires whichis connected to the set is over the strips 9, 10 and underneath theinsulating layers 11, 12.

In FIG. 2, the layer 11 is represented partially removed to show thestrip 9 connecting the active zones to the wire 5, whereas the layer 12is not removed in the illustration, hence the strip 10 which isunderneath the layer 12 is represented in dashed line.

In some embodiments, a gel layer is added on the active zones 7, 8 toimprove the conductivity and also on the insulating layers 11, 12. Thegel layer could be a continuous layer or could be made of gel stripsadded mainly on the active zones.

As one will readily understand, the configuration illustrated in FIG. 2is only one specific non-limitative realization and equivalent variantscan be considered.

These variants will be described hereunder by identifying the successivelayers forming the set according to the present invention.

The first layer can be a backing layer (non conductive layer, forexample made of PVC or PP or a fabric) on which a conductive layer (forexample of carbon) is placed. The contacting means (for example wires)may be placed between the backing layer and the conductive layer, or onthe other side of the conductive layer with respect to the backinglayer. In this variant, the conductive layer is cut to the desired shapethus directly forming the active zones. A conductive ink (for examplesilver based) may be deposited on the active zone cut into theconductive layer.

In this embodiment with a conductive layer, a screen non-conductivelayer can be added to cover the parts of the conductive layer thatshould not contact the body of the user and also the wires if they areon the other side of the conductive layer with respect to the backinglayer.

In another embodiment, the backing layer is made of a non-conductivelayer (PVC, PP for example or a fabric) or of a non-conductive orlow-conductive carbon layer and the active zones are made directly bythe deposition of conductive ink on said backing layer or carbon (whichdoes not have to be cut). In this embodiment, the contacting means (i.e.wires) can be placed over the conductive ink or between the ink and thenon-conductive layer for electrical connection. If the wires are placedover the conductive ink (that is on the side of the body of the user),then a non-conductive screen layer can applied for covering the contactzone between the wires and the active zones in the manner taught in FIG.2.

In FIG. 3A, a cut view along axis A-A of FIG. 2 is illustrated. The setis made of a first non-conductive layer of fabric 3 and a conductivelayer 6 (for example carbon) on which the active zones 7, 8 are madewith conductive ink. Optionally, as indicated above and represented inFIGS. 3A and 3B, the set may further comprise an insulating layer suchas a screen 11, 12 and a gel layer 13 (represented in FIG. 3B).

The conductive layer is also optional and the active zones may be placeddirectly on the first non-conductive layer.

As indicated above, the conductive ink deposition is optional and in asimple configuration, one can use only a carbon conductive layer whichhas be cut to form the desired active zones shapes with contacting meanssuch as wires connected to either side of the carbon layer.

Size parameters are illustrated in FIG. 4 which shows a schematicalpartial view of a set according to FIG. 1 or 2. In this example, theactive zones are referenced 7 and 8 as in FIG. 2 but the principleexplained in the following related to the sized and distances apply toall embodiments of electrode sets of the present invention.

In some embodiments, sizes for the lateral dimensions (D₂) of the activezones 7, 8 are from 1 mm to 40 mm and for the spacing (D₁) betweenactive zones 7, 8 are from 1 mm to 40 mm.

In one embodiment, D₁ and D₂ are at least 2 mm.

In another embodiment D₁ and D₂ are about 5.5 mm.

In a further embodiment, D₁ and D₂ are about 3 mm.

In the embodiment of FIGS. 1 and 2, the set has a longitudinal size ofabout 130 mm and a lateral size of about 60 mm.

Of course, all these dimensions may be adapted depending on theconfiguration of the set chosen in among the variants described hereinand also, in a given set of electrodes, the values of D₁ and D₂ may bevaried so that the electrodes and the spacings may have different sizes.

Experimentally, it has been shown that these sizes were particularlyadvantageous for applying a TENS stimulation. Indeed, one has noticedthat with the electrode set construction according to the invention, thethresholds of TENS or EMS stimulation (i.e. sensory vs. muscular) werewell differentiated, whereas with a classical construction such as withlarge electrodes which are spaced apart, these thresholds were muchcloser and much more difficult to differentiate.

In the present specification the TENS threshold is understood as meaningthe minimum current required to effectively reach and stimulate sensoryfibers/nerves and the MOTOR threshold is the amount of current requiredto reach and stimulate the muscle fibers/nerves.

This differentiation effect is demonstrated in the Tables 1.1-1.3 (FIGS.16A-16C), 2.1-2.3 (FIGS. 17A-17C), and 3.1-3.3 (FIGS. 18A-18C), in whichthe measurements provided show that with the electrode set according tothe present invention, one obtains a ratio between the thresholds ofTENS and MOTOR stimulation of up to 10 for small and close to each otheractive zones and a ratio of 1 for larger active zones which are distant.

With a well differentiated threshold, it is thus possible to increasethe TENS treatment dosage, without reaching an undesired MOTORstimulation. Hence the treatment is improved and more effective.

These tables are examples of TENS thresholds, MOTOR (muscular)thresholds and the ratio of both thresholds for three different testpatients (first patient tables 1.1 to 1.3 (FIGS. 16A-16C), secondpatient tables 2.1 to 2.3 (FIGS. 17A-17C) and third patient tables 3.1to 3.3 (FIGS. 18A-18C)). The columns define the active zone spacing D1in mm, the lines define the active zone lateral dimension D2 in mm, andthe values indicated in the tables are the current threshold in mA forTENS stimulation (Tables 1.1, 2.1, 3.1; FIGS. 16A, 17A, and 18A),current threshold for MOTOR stimulation (Tables 1.2, 2.2, 3.2; FIGS.16B, 17B, and 18B) and the ratio EMS/MOTOR thresholds (Tables 1.3, 2.3,3.3; FIGS. 16C, 17C, and 18C). The electrode width is 50 mm.

Typical signals used include a succession of a high frequencystimulation followed by a low frequency stimulation. For the tablesshown in FIGS. 16A-18C, the high frequency signal has the followingparameters:

-   -   impulse width: 60 μs    -   frequency: 120 Hz    -   duration: 3 s

The low frequency signal has the following parameters:

-   -   impulse width: 60 μs    -   frequency: 2 Hz    -   duration: 3 s

The results given are typical of the values obtained when the electrodesare placed on different parts of the body of the patient.

As one can clearly see, the ratio increases if the electrodes sizediminishes and also the distance between the electrodes diminishes.However, it has also been shown experimentally that if the values of D1and D2 are too small, in particular less than 1 mm, the effect is notpresent anymore because the current does not reach the sensory fibersbut goes directly from one pole to another (see for example the “nosensitive” effect mentioned further in the description and illustratedin FIG. 15).

Hence, a TENS treatment using the set according to the invention is muchmore effective since the TENS and MOTOR thresholds are well separated.

Accordingly, the range of current values that can be selected for a TENSstimulation without reaching the MOTOR threshold is larger and the TENStreatment is more efficient because it can apply higher intensitieswhich are more efficient.

An advantage of the invention is the following: to overcome adaptation,the user may for example increase the stimulation current withoutreaching the MOTOR threshold.

A second advantage is to avoid pain, when the user has muscle pain.Again, an unwanted muscle stimulation is avoided. Indeed, muscletwitches or tetanic contractions are undesired for daily living. Theinvention thus provides a better use of TENS stimulation for a longerperiod, which amounts to better pain relief.

A third advantage resides in the simplicity of the system: placingelectrodes where it hurts, as opposed to placing multiple electrodesaround a painful area as taught in the prior art. Since the deliveredcurrent will not penetrate the tissue deep enough to stimulate themuscle, thereby neither aggravating an injured muscle nor causing pain,the electrode set can be placed directly on the painful area.

FIG. 5 shows another embodiment of the invention. In this embodiment,the set of electrodes is made of several layers of different materials,some of the them comprising cut or punched out holes/openings to formthe active zones.

This embodiment comprises a first non-conductive backing layer 20,similar to the backing layer 3 described above. Such backing can be afabric backing and may be oversized to improve adhesion to the skin.

On this layer 20, a second conductive layer 21, for example, a carbonconductive layer (or another equivalent material) is placed, said layer21 being connected to a wire 5.

Over this layer, a third layer 22 is placed, this layer 22 having aconductive side 22A, for example a carbon layer or another equivalent,connected to a wire 4 and a non-conductive side 22B for example a layerof PVC or PP or another equivalent material. The non conductive side 22Bis on the side in contact with the conductive layer 21. This side of thelayer 22 is rendered non-conductive for example by the application of athin foil of non-conductive material. Other equivalent solutions are ofcourse possible. This third layer 22 as a mask comprises openings 23that allow contact with the layer 21, these contact zones beingillustrated in dashed lines on layer 21.

Over this third layer, a fourth non-conductive layer (for example madeof PVC or PP or another equivalent material) is provided as a top mask24. This top mask also has two groups of openings 25, 26, the firstgroup of openings 25 being aligned with the openings 23 of the thirdlayer 22 as illustrated by the vertical dashed lines and the secondgroup of openings which only allow contact with the third layer 22.

This construction allows the formation of an electrode set withneighboring active zones, according to principle of the presentinvention, through the openings made in the different layers.

For the sake of illustration, these active zones have been schematicallyrepresented in FIG. 5 with dashed lines and are referenced 27 and 28.The principles described above relating to the lateral sizes of theactive zone (D2) and the distance between active zones (D1) applycorrespondingly to this embodiment. In addition, FIG. 5 is anillustration of an embodiment where the number of active zones (and ofopenings) can be varied with respect to what is shown. There can be moreor less active zones than represented and also an even or odd number ofactive zones.

A gel layer is added on the top mask 24, said gel being either a uniformlayer deposited on the entire surface or a layer cut and/or depositedselectively only on the active zones.

The principle of the present invention may be used with other shapes ofactive zones, for example, circular, in which case the set could made ofa number of concentrical circular active zones. In other variants, theactive zone may have an oval shape or any other shape or conformationsuitable for application to the body. Such other shapes andconfiguration are illustrated in FIGS. 6A to 6D by way of non-limitingexamples with the distances D₁ and D₂.

For example, FIG. 6A shows a checkerboard configuration of active zones;in FIG. 6B the active zones are circular and disposed in a matrix-likearrangement. FIGS. 6C and 6D illustrate schematically otherconfigurations.

FIGS. 7A and 7B schematically show other particular embodiments of theinvention. In the embodiment of FIG. 7A, each active zone 30-33 isconnected to a source (for example a stimulator, not represented)through switches 34-37 allowing the connection of any combination ofactive zones or pairs of active zones to a source by actuation of theswitches.

In the embodiment of FIG. 7B, each active zone 40-43 is independentlyconnected to a source (for example a stimulator, not represented)allowing also an independent activation of each single active zone40-43. In this embodiment, one has also represented a tab 44 that couldbe used for connection of the set of electrodes to a stimulator, forexample, either directly or via a cable or even via a wireless system.The selection of the active zones being activated can then be made atthe stimulator level, for example, by specific stimulation programs.

The configuration illustrated in FIG. 7B is interesting in that itallows the activation of each active zone independently. This is usefulwhen one wants to apply a TENS stimulation or an EMS stimulation withthe same electrode set.

For example, for a TENS stimulation, active zones 40 and 42 can formnegative poles and zones 41 and 43 form positive poles in accordancewith the principle of the present invention. For an EMS stimulation,zones 40 and 41 would form a negative pole and zones 42 and 43 andpositive pole thereby forming active zones with a larger surface.

Of course, it is possible to invert the poles with respect to thedescription given above for FIG. 7B, the aim being of having either asuccession of alternating poles (for TENS stimulation) or two poles eachmade of a group of neighboring active zones.

This could also be realized with the configuration of FIG. 7A if allactive zones were connected via switches (such as switches 34-37) to thelines “+” and “−”.

Of course, the embodiments of FIGS. 7A and 7B are only for illustrativepurposes and the configurations are not limited to four active zones:more zones may be present, for example 6, 8, 10, 12, etc. Also theprinciples illustrated in FIGS. 7A and 7B (individual connection of eachactive zone) may be applied to the other electrode set configurationsand stimulators as described in the present specification or covered bythe claims.

In FIG. 8, a particular application of an electrode set of the presentinvention is illustrated. In this figure, the set is configured withseveral ring shaped active zones 50-53 (of course other shapes may beenvisaged) connected to wires 54, 55. As depicted, zones 50 and 52 areconnected to wire 55, and zones 51 and 53 are connected to wire 54.Central zone 50 comprises an opening 56 to allow passage of a needle 57of a syringe 58. In this embodiment, one may utilize the principle ofthe invention to create a local anesthesia by maximizing the sensoryeffect against pain of the device as described in the gate-controltheory of pain described in the article of Mark Johnson mentioned above.One can thus take advantage of this local anesthetic effect to, forexample, stick the needle 57 of the syringe 58 or a drip (notrepresented) at this place or even perform surgery. However, as shown,the active zones should be slightly modified in this embodiment toinclude at least the opening 56 through which the needle or a surgicalinstrument may pass. Of course, this embodiment may apply to all activezone configurations, in particular to the one illustrated in the presentapplication, as long as it is possible to stick a needle at the desiredplace (for example by creating an opening). It is of course alsopossible to avoid this opening and stick the needle (or a surgicalinstrument) between active zones.

The anesthetic effect may also be useful for superficial skinoperations, for example, to remove a pimple or a mole, a melanoma(suspected or real) for a biopsy or for suture. For such applications,one should provide an opening of consequence in at least one of theactive zones in application of the principle represented in FIG. 8, orsuch operations may also be carried out between neighboring activezones. For example, the configuration illustrated in FIG. 6D could beused to this effect, or another configuration illustrated in the presentapplication.

In a further embodiment, the principle of which may be applied to allembodiments described above, one can integrate at least a part of thecircuit of the stimulator on the set of electrodes allowing to connectdirectly the stimulator on the support. Indeed, in certainconfigurations and depending on the number of electrodes and sets, theuser may end up with a device carrying many wires (at the maximum equalto the number of individual active zones if one chooses theconfiguration of FIG. 7B) which then will be complicated to connectproperly, a problem which creates an error source. By choosing anintegrated circuit or a plug-in system for the stimulator, one overcomesthis problem of the multiplication of individual wires and can attain aconfiguration with a reduced number of wires. This alternative isillustrated in FIGS. 9A and 9B with electrode sets 60, 62 andstimulators 61, 63. Of course, the sets 60, 62 represented are onlygiven as a non-limiting examples, and any configuration represented inother drawings of the present application or made according theprinciples of the present invention may be used as a set of electrodes.In addition, in FIG. 9B, a stimulator 63 can be attached by any suitablemeans (clipping, Velcro®, etc.) to the set for example, by snapconnectors. In this case, it can be advantageous to use the snapconnectors as direct contact means for electrical connection of thestimulator to the wire of the set. The use of the device according tothe invention is thus made easier and the user needs only to snapstimulator 63 to electrode set 62 without connecting additional wires.

Another aspect of the invention is related to a method for dimensioningthe set of the invention. In this method, one uses the electrode set asdefined above with a gel layer between the set and the skin of the userand the principles of the dimensioning method are disclosed below withreference to FIGS. 10A-15. A typical example of such an electrode set isthe one represented in FIGS. 2 and 3B.

FIGS. 10-15 illustrate the hypothesis and models considered in thisdimensioning method. The idea is to maximize the resistivity of the gelin the direction X, Y (Rxy) in order to force the current to penetrateinto the body of the user, rather than go through the gel directly fromone electrode to a neighboring electrode.

The values of resistivity in both directions are defined as follows(with reference to FIGS. 10A and 10B):

${{Rxy} = {\rho_{GEL}*\frac{D_{1}}{e*l}}},$where ρ_(GEL) is the specific resistivity of the gel

${Rz} = {\rho_{GEL}*\frac{e}{D_{2}*l}}$

The resistivity of the body is defined as follows:

$R_{BODY} \cong {2*\frac{R_{SPEC}}{\frac{D_{2}*l}{2}}}$R_(SPEC)≅10 kΩcm² is the specific resistivity measured from the surfaceof the skin at the considered frequencies of stimulation. Of course,this value may change according to the circumstances.

Considering the electrical diagrams of FIGS. 11-14, one can define thefollowing equation for the currents:

$\frac{I_{body}}{I} = {\frac{I_{body}}{I_{body} + I_{Rxy}} = \frac{1}{1 + \frac{IRxy}{I_{body}}}}$

Accordingly, what is sought is to minimize the ratio I_(Rxy)/I_(body)

It has been found that:

${\frac{I_{body}}{I} = {50\%}},$

-   -   if this ratio is equal to 1, then meaning that 50% of the        current is lost in the gel;

${\frac{I_{body}}{I} = {10\%}},$

-   -   if this ratio is equal to 9, then meaning that 90% of the        current is lost in the gel;

We have then the following equation:

$\begin{matrix}{\frac{I_{Rxy}}{I_{body}} = {\frac{{2R_{Z}} + R_{body}}{R_{XY}} = {{{2*\frac{R_{Z}}{R_{XY}}} + \frac{R_{body}}{R_{XY}}} = {{2*\frac{e^{1}}{D_{1}D_{2}}} + \frac{4*R_{SPEC}*e}{\rho_{GEL}D_{1}D_{2}}}}}} & (1)\end{matrix}$

In some embodiments, ρ_(GEL)≅10-100Ω.

As one can see, this equation has two members, one purely geometrical(e, D₁ and D₂) and a second member which is linked to the resistivity(body and gel).

To sum up, one wishes to optimize three parameters (see FIG. 15):

1) low loss in the electrode set, this parameter being optimized by theequation (1) above

2) no motor stimulation of muscle, this aspect has been discussed above,where it has been shown experimentally that the lateral size of theactive zones D₂ and the distance D₁ between two neighboring active zoneswere important to optimize the threshold ratio between the TENS effectand the MOTOR effect. In particular, one has demonstrated that D₁ and D₂have to be a minimum in order to maximize this threshold ratio.

3) no “no sensitive”, meaning the absence of any TENS effect because thecurrent does not go deep enough in the skin or remains in the gel layerwithout penetration of the skin. For this third parameter, it has beenshown that active zones which are too small and too close to one anotherhave this effect, in particular observed when D₁=1 mm and D₂=1 mm. Onecan assume that smaller size values will further increase this effect.

FIG. 15 represents visually three possibilities of stimulation.Considering the drawings from the left to right, the first one shows asituation in which the current goes too deeply in the skin andstimulates the sensitive nerves and also the muscle nerves, the seconddrawing shows the optimal situation in which only the sensory nerves arestimulated and the third drawing shows another undesired situation whereno nerves are stimulated at all.

From the above, one will understand that if the electrode set is usedwithout a gel layer entirely covering the side of the set that is incontact with the skin of the user for example with gel strips, theexperiments and values disclosed in the above mentioned Tables (shown inFIGS. 16A-18C) give a basis of optimum sizes for the active zones andtheir relative position, whereas if a continuous gel layer is placed onside of the set in contact with the skin of the user, it is necessary tofurther consider the equation (1) indicated above to optimize the valuesand take this layer into account.

Of course, all values mentioned above are indicative and may be variedaccording to the circumstances to dimension an electrode set accordingto the present invention. The present invention thus also provides amethod for dimensioning an electrode set using the equation andparameters set above, and also to an electrode set obtained by saidmethod.

As can be readily understood from the above description, the presentinvention also concerns a method of treatment using the definedelectrode set and a method of use of such electrode set. More precisely,the device according to the invention is used for a TENS treatment ofthe human body for example for pain relief.

Such methods include at least the steps of applying the set ofelectrodes to the body of a user and activating the zones with a givensignal in order to obtain the desired TENS stimulation. In anotherapplication, the electrode set can be used for anesthesia as describedabove.

In these methods, at least the following steps are carried out:

-   -   applying an electrode set with active zones to a user;    -   connecting the stimulator to the set;    -   applying electrical signals to the user through the active        zones.

As can be readily understood from the present specification, theapplication of the electrode set is made on the treatment location (forexample directly on the painful area or where the surgical operation istaking place). Accordingly, the shape and the size of the set and/or ofthe backing (if present) can be tailored to the shape of the body tooptimize the application. Typical examples include, leg, arm, knee,elbow etc.

Then the set of electrode is connected to the stimulator. This can bemade by a direct connection of the stimulator to the set or by wires. Aswill be understood from a skilled reader, the connection to thestimulator may be carried out before the electrode set is applied to theuser.

Then, the desired signals are applied by the stimulator to the electrodeset.

The signals may be predetermined and memorized in the stimulator (forexample predetermined stimulation programs) or they may be chosen by theuser and adapted during use.

The stimulator may be connected to the electrode set once the set hasbeen applied to the user, or it may be connected beforehand and then thestimulator is applied to the user.

Typical TENS examples of signal values (amplitude, frequencies waveformsetc) can be taken from the publication “Transcutaneous Electrical NerveStimulation (TENS)” of Mark Johnson referenced above in the presentspecification.

As can be understood, the embodiments described above are given by wayof non-limiting examples and equivalent variations are possible, forexample on the shapes of the electrodes and their number which are notlimited to the one represented in the figures. The wires used ascontacting means may be connected in any suitable fashion, by gluing orother connection means mechanical or not (connectors, snaps etc.) Ofcourse, the spacing D₁ and the size D₂ may not be constant in a set: onemay combine different configurations in the same electrode set and usedifferent values for D₁ and D₂.

In addition, the values D₁ and D₂ indicated above can similarly beapplied on the other shapes of electrodes as mentioned above and asillustrated in the drawings.

It is understood that the embodiments discussed and represented in thedrawings are for illustrative purposes and should not be interpreted ina limiting way. In addition, the principles exposed above apply to allthe configurations represented. For example the principle of theembodiment of FIG. 5 could be applied to active zones with differentshapes as illustrated in other figures of the present application.

In addition, the shape and/or configuration of the electrode said mayalso be chosen depending on the part of the user's body being stimulated(arm, torso, leg, foot, knee, elbow etc) so many different shape, sizesand number of active zones may be envisaged within the scope of thepresent invention. Also, as mentioned above, the size D1 and spacings D2may be maintained constant in a given set or may be varied in the saidset. This choice may depend on the desired position of the set on thebody and/or the type of treatment envisaged.

From the above, it will be readily understood that many differentconfigurations might be envisaged and are covered by the presentapplication. For the active zones, many equivalent suitable conductivematerials (in addition to carbon) may be envisaged.

In addition to the embodiments described above, it is also possible, asan illustrative example, to form an electrode set with only a part ofthe active zones having the dimensions and distances described in thepresent specification. For example, some active zones could have alarger lateral size (i.e. D₂ over 40 mm) and in between such activezones, a set according the present invention could be placed.

In a further embodiment, using the grouping of active zones describedabove, it can be envisaged to form a set with active zone having alateral size of less than 1 mm and also a distance than less than 1 mmbetween such neighboring active zones, and by grouping such activezones, one obtains an overall active zone lateral size betweenapproximately 1 mm to 40 mm and a spacing also between approximately 1mm to 40 mm.

The invention claimed is:
 1. An electrode, comprising: a first layercomprising a non-conductive material; a second layer disposed on atleast a portion of the first layer, the second layer comprising aconductive material; a third layer disposed on at least a portion of thesecond layer, the third layer including a non-conductive side in contactwith the second layer, a conductive side opposite the non-conductiveside, and a plurality of openings formed through the third layer toexpose a plurality of electrically active zones of the second layer; anda fourth layer disposed on at least a portion of the third layer, thefourth layer including a non-conductive material, a first plurality ofopenings formed through the fourth layer and aligned with the pluralityof openings of the third layer so as to expose the electrically activezones of the second layer, and a second plurality of openings formedthrough the fourth layer to expose a plurality of electrically activezones of the third layer.
 2. The electrode of claim 1, wherein theelectrically active zones of the second layer and the electricallyactive zones of the third layer are arranged to form a succession ofpoles of alternating polarity or to form groups of poles of alternatingpolarity.
 3. The electrode of claim 2, wherein at least one of theelectrically active zones of the second layer or the third layer has alateral size of 1 mm to 40 mm, and wherein a spacing between adjacentelectrically active zones of the second layer and the third layer is 1mm to 40 mm.
 4. The electrode of claim 3, wherein the lateral size andthe spacing are approximately 5.5 mm.
 5. The electrode of claim 3,wherein the lateral size and the spacing are approximately 3 mm.
 6. Theelectrode of claim 1, wherein the conductive material of the secondlayer comprises carbon.
 7. The electrode of claim 1, wherein theconductive side of the third layer comprises a layer of carbon.
 8. Theelectrode of claim 1, wherein the first layer comprises: anon-conductive layer, and a conductive layer disposed on thenon-conductive layer.
 9. The electrode of claim 8, wherein thenon-conductive layer comprises a foil of non-conductive material. 10.The electrode of claim 1, wherein the non-conductive material of thefirst layer comprises a polypropylene material, a polyvinyl chloridematerial, or a fabric.
 11. The electrode of claim 1, wherein thenon-conductive material of the fourth layer comprises a polypropylenematerial, a polyvinyl chloride material, or a fabric.
 12. The electrodeof claim 1, further comprising a gel layer disposed on the fourth layer.13. The electrode of claim 1, further comprising a gel layer disposed onthe electrically active zones of the second layer and the third layer.14. The electrode of claim 1, wherein the electrode set is configured toprovide a current to a body which reaches and stimulates sensory fibersand which does not reach and stimulate muscle fibers.
 15. The electrodeof claim 1, wherein the electrode set is adapted to interface with anexternal surface of a patient's body to deliver TENS stimulation. 16.The electrode of claim 1, wherein the electrode set is adapted tointerface with an external surface of a patient's body to deliver EMSstimulation.
 17. An electrode set for a stimulation device, theelectrode set comprising: a plurality of neighboring electrically activezones of alternating polarity and configured to provide current to abody which reaches and stimulates sensory fibers and which does notreach and stimulate muscle fibers, the electrically active zones definedby a plurality of layers including at least a first layer configured tobe set to a first polarity, at least a second layer configured to be setto a second polarity, opposite the first polarity, and openingsconfigured to expose portions of the first layer and the second layer;wherein at least one of the plurality of electrically active zones has alateral size of 1 mm to 40 mm; and wherein a spacing between neighboringelectrically active zones is 1 mm to 40 mm.
 18. The electrode set ofclaim 17, wherein the plurality of layers further comprise anon-conductive layer, and wherein the openings comprise: a firstplurality of openings formed through the non-conductive layer and thesecond layer so as to expose the portions of the first layer, and asecond plurality of openings formed through the non-conductive layer toexpose portions of the second layer.
 19. The electrode set of claim 18,wherein the plurality of neighboring electrically active zones comprise:the portions of the first conductive layer; and the portions of thesecond conductive layer.
 20. The electrode set of claim 17, wherein thelateral size and the spacing are approximately 3 mm or approximately 5.5mm.